Phosphazene fire retardants

ABSTRACT

IMPROVED FIRE RETARDANT PHOSPHONITRILATE POLYMER COMPOSITIONS HAVING TWO CYCLIC OLIGOMERIC PHOSPHONITRILATE COMPOUNDS, SUCH AS HEXAPROPOSYPHOSPHRAZENE, CROSSLINKED BY OXYGEN FROMING A P-O-P BOND. THE CROSSLINKED PHOSPHONITRILATE COMPOUNDS ARE PREPARED BY REACTING A CHLOROPHOSPHAZENE WITH A METAL ALCOHOLATE, PREFERABLY SODIUM PROPOXIDE, AND AN ALKALI METAL HYDROXIDE, PREFERABLY SODIUM HYDROXIDE.

United States Patent O 3,795,526 PHOSPHAZENE FIRE RETARDANTS Charles R.Bergeron, Baton Rouge, La., assignor to Ethyl Corporation, Richmond, Va.No Drawing. Filed Aug. 30, 1972, Ser. No. 285,007 Int. Cl. C08b 21/20,21/22; C09j 3/04 US. Cl. 106-168 8 Claims ABSTRACT OF THE DISCLOSUREImproved fire retardant phosphonitrilate polymer compositions having twocyclic oligomeric phosphonitrilate compounds, such ashexapropoxyphosphazene, crosslinked by oxygen forming a POP bond. Thecrosslinked phosphonitrilate compounds are prepared by reacting achlorophosphazene with a metal alcoholate, preferably sodium propoxide,and an alkali metal hydroxide, preferably sodium hydroxide.

BACKGROUND OF THE INVENTION Phosphonitrilate polymers are known to befire retardants for cellulosic materials; U.S. 3,455,713, Godfrey, Ind.Eng. Chem. Prod. Res. Develop, 9, No. 4 (1970), pp. 426-436, SouthAfrican 70/2,767, US. 2,892,803. Such polymers are made by reactingsodium derivatives of monohydric alcohols with phosphonitrilicchlorides. Alternatively, the monohydric alcohols can be reacted withthe phosphonitrilic chloride as described in Netherlands 7106772.

For some processes for making flame retardant rayon, phosphonitrilatesof increased viscosity are desirable. Also, greater retention of thephosphonitrilate polymer in the fiber after forming it and duringlaundering is desirable. The cross-linked phosphonitrilates of thisinvention have higher viscosity than phosphonitrilates which are notcross-linked. They also have higher phosphorus content. Otheradvantageous properties will be apparent from the following descriptionof the invention.

SUMMARY OF THE INVENTION One aspect of this invention provides aphosphonitrilate polymer composition comprising two cyclic oligomericphosphonitrilate compounds being cross-linked by oxygen forming a PO-Pbond.

Another aspect of this invention provides a process for preparing thephosphonitrilate polymer which has two cyclic oligomericphosphonitrilate compounds crosslinked by oxygen forming a POP bond byreacting a chlorophosphazene with a metal alcoholate and from about 0.1to about 10 percent by weight of an alkali metal hydroxide based on saidalcoholate.

Another aspect of the invention provides cellulosic materials whose fireretardance is enhanced with such polymers. Such materials may be madefire retardant by the padding technique; i.e., treating the surface withthe polymer or solution or suspension thereof and then drying. As apreferred embodiment of this invention, this invention providescellulose filaments or filamentary articles having dispersed therein aflame retardant amount of such polymers. These can be made by viscoseand a flame retardant amount of such polymer, shaping the mixture into afilament, and coagulating and regenerating said filament.

DESCRIPTION OF PREFERRED EMBODIMENTS Phosphazene compounds are ring orchain phosphorusnitrogen compounds having two substituents connected toeach phosphorus atom, but no substituents on nitrogen, and arecharacterized by a valence-unsaturated skeleton. Phophonitrilatecompounds are phosphazenes in which ice the substituents on thephosphorus atom are alkoxy or aryloxy radicals and have the generalformula where a is at least 3 and R can be the same or different alkylor aryl radicals having up to about 6 carbon atoms.

Processes for producing phosphonitrilates result in a mixture ofcompunds, usually oligomers such as the cyclic trimer, tetramer,pentamer and linear polymers. According to this invention, the cyclicoligomers are cross-linked by oxygen forming a P-OP bond. This can beillustrated by the following general formula showing two cyclic trimericphosphonitrilates joined by a bridging oxygen atom connecting aphosphorus atom on each of the trimers.

30 OR RO OR Of course three, four or more cyclic oligomers can becross-linked in a similar manner. Not only can two or more cyclicoligomeric phosphonitrilates be cross-linked by oxygen forming a POPbond, but cyclic-linear and linear-linear oligomeric cross-linking isalso contemplated by this invention. One skilled in the art can envisionnumerous possibilities for cross-linking various cyclic and linearoligomers. Also, as when three or more oligomers are cross-linked, morethan one P-OP bond connecting a single oligomer to other oligomers iscontemplated, resulting in a complex pattern of many interlocked chainsand rings and mixtures thereof.

While the phosphonitrilate polymer of this invention may have mixturesof any of the above oxygen crosslinked oligomers, a preferredcomposition is one in which at least one of the phosphonitrilatecompounds is an alkoxyphosphazene. Another preferred composition is onein which at least one of the cyclic oligomeric phosphonitrilatecompounds is a cyclic trimer. Even more preferred is a composition inwhich at least one of the cyclic oligomeric phosphonitrilate compoundsis cyclic trimeric hexaalkoxyphosphazene. Still more preferred is acomposition having at least two cyclic oligomeric phosphonitrilatecompounds being cross-linked by oxygen form ing a POP bond. A furtherpreferred composition is one having two cyclic trimeric hexaalkoxyphosphazene compounds cross-linked by oxygen forming a POP bond. Mostpreferred is a composition in which at least one of the cyclicoligomeric phosphonitrilate compounds is hexapropoxyphosphazene.

It has been found that the phosphonitrilate polymers of this inventioncan be prepared by reacting a phosphonitrilic halide, such as thechloride, with an alcohol reactant, preferably the alkali metalalcoholate, and an alkali metal hydroxide.

The nature of the phosphonitrilate polymer of this invention depends inpart on the nature of the phosphonitrilic starting material. The mostpractical starting material is a phosphonitrilic chloride wherein a isat least 3. These can be formed by any method known in the art.Exemplary methods are in Am. Chem. 1., 19, 782 (1897), Schenk et al.,Ber., 57B, 1343 (1924),

3 US. 2,788,286, 2,008,799, 3,249,397, 3,347,643, 3,367, 750, 3,372,005,3,378,353, 3,379,511, 3,407,047, 3,462,247, 3,359,080, Netherlands7005128 and J. Chem. Soc. (A), pp. 768-772 (1971).

The alcohol reactant includes both the alcohol itself and the alkalimetal alcoholate derivative, the latter being preferred. Monohydricaliphatic and aromatic alcohols can be used. Of the monohydric aliphaticalcohols, those having up to six carbons are preferred. However, thosehaving 7, 8 or more carbons can be used if desired. Of the monohydricalcohols, exemplary preferred species are methanol, ethanol,isopropanol, n-propanol, n-butanol, neopentyl alcohol, n-hexanol,2-hexanol, mixtures thereof, and the like. Monohydric aromatic alcoholsused include phenol and its substituted derivatives. For mostpreparations reaction of metal derivatives of the alcohols is preferredover reaction of the alcohols themselves.

Of the metals, the alkali metals are preferred. Sodium and potassium arehighly preferred because of their availability, and sodium is mostpreferred because of its reactivity and relative inexpensiveness. Themetal derivative is prepared by reacting the metal with a hydroxycompound in any convenient manner. For example, sodium can be reactedwith an alcohol using an inert hydrocarbon such as benzene or heptane asa reaction medium. The sodium may be in the solid state or maypreferably be melted by heating to about 110 C. When using moltensodium, it is convenient to employ a reaction medium which has a boilingpoint above the solidification temperature of the sodium. Toluene,kerosene, or No. 9 oil can be employed. Kerosene or No. 9 oil may besomewhat difficult to remove from the product, and accordingly, tolueneis a reaction medium of choice.

It is convenient to use an excess of a hydroxy compound as a precautionagainst unreacted sodium. Good results are obtained utilizing a 1-10weight percent excess. However, greater or lesser excesses can be used.If the reaction is conducted utilizing a molten metal, then it isconvenient to add the hydroxy compound at a rate in which the heat ofreaction will keep the metal molten. Toward the end, the reaction isslower and stirring and heating can be efficaciously employed. Thereaction is continued until hydrogen evolution is complete andessentially no metal remains.

The alkali metal hydroxide is preferably sodium or potassium hydroxide,with the sodium hydroxide being more highly preferred. Only a smallamount of alkali 'metal hydroxide is required, depending on the desireddegree of oxygen cross-linking. From about 0.1 to about 10 percent byweight based on the alcoholate is reacted with the phosphonitrilichalide (e.g., chlorophosphazene). Preferably, the alkali metal hydroxideis present at from about 2 to about 6 percent by weight based on saidalcoholate.

Although the alkali metal alcoholate and hydroxide can be preparedseparately and then reacted With the chlorophosphazene, a particularlypreferred aspect of this invention is to prepare both at the same timeby mixing water with the alcohol and adding the mixture to the moltenalkali metal. This procedure provides a mixture of alkali metalalcoholate and alkali metal hydroxide which can be reacted with thechlorophosphazene.

Except for the presence of the alkali metal hydroxide, the preparationof the phosphonitrilate proceeds normally according to the methodsreferred to hereinabove. The reaction mixture which contains thesolvent, e.g., benzene, toluene or heptane, any excess unreatedmonohydric alcohol, e.g., propanol, the metal alcoholate, e.g., sodiumpropoxide, and the alkali metal hydroxide, e.g., sodium hydroxide, isreacted with the phosphonitrilic halide. It is preferred that the totalof sodium propoxide and sodium hydroxide be in excess over thetheoretical requirement. usually two molecules of alcohol for each unitof chlorophosphazene. In this instance, a total excess of sodiumalcoholate and hydroxide of from about 5 to about 4 weight percent overthe theoretical requirement is conveniently employed.

In many instances, the reaction is rapid and exothermic at the beginningand requires no heating. After mixture of the reactants is complete itmay be convenient to heat the resultant reaction mass and hold it atreflux temperature for such time as analysis indicates completereaction. Reaction times in the range of from /2 to 10 hours can beused. This is somewhat dependent upon the reaction temperature which isusually within the range of from ambient to 110 C.; more preferably fromabout 55 to 110 C.

After conduction of the reaction, the excess free hydroxy compound andthe solvent are removed by distillation or other suitable means. Thesecan be recycled for later use.

As with the preparation of the metal derivative of the hydroxy compoundthe phosphazene synthesis proceeds well at ambient pressure.Accordingly, atmospheric pressure is of choice. However greater orlesser pressures can be used if desired.

It is to be understood that mercaptides can be used in a fashion similarto that described above to prepare the sulfur compounds analogous to theabove-described phosphazenes.

After removal of the free hydroxy compound and solvent, it is convenientto isolate the product from the resultant mass by water-washing followedby stripping the remainder of the solvent. In many instances, bestresults are obtained by using plurality of water washes. In manyinstances, two washes will suffice. For precaution against emulsionsduring washing, it is preferred to have the water washes conducted suchthat the water has a pH of 9 or higher. Water-washing is employed bymixing the phosphazene product with water and agitating. Typicalagitating times are 10 to 20 minutes but shorter or longer times can beemployed, if desired. If in the first Water wash, a rag layer appears,it can be left with the organic layer for a subsequent wash. If emulsionappears in the second wash, sodium chloride or other salt can be addedto increase the density difference between the phases.

After water-washing and separating, the organic layer can be subjectedto distillation to remove solvent.

From the preceding description, a preferred embodiment of this inventionis a process for preparing the phophonitrilate polymer compositiondescribed above comprising reacting in a hot inert solvent a cyclicoligomeric chlorophosphazene with a metal alcoholate and from about 0.1to about 10 percent by weight of an alkali metal hydroxide based on saidalcoholate. In a more highly preferred embodiment, said reacting ischaracterized by the slow addition of said metal alcoholate and saidalkali metal hydroxide to said chlorophosphazene. Slow addition ispreferred to allow the smaller amount of alkali metal hydroxide to formtheP-O-P bonds cross-linking the phosphonitrilate polymer. By slowaddition is meant addition over a period covering from about 10 to about30 percent of the total reaction time EXAMPLE A mixture of sodiumpropoxide and sodium hydroxide was made by adding 500 parts of heptaneand 49 parts of sodium to a clean, dry reaction vessel. The reactionvessel was heated at atmospheric pressure and with agitation to about100 C. The sodium melted, forming a dispersion in the heptane. To thisdispersion was added dropwise 114 parts of n-propanol and 3.5 parts ofwater forming a slurry of sodium propoxide and sodium hydroxide inheptane,

In another clean, dry reaction vessel, after flushing with nitrogen, wasadded 116 parts of chlorophosphazene (PNCl where x=3.7, dissolved in 126parts of monochlorobenzene. This solution was heated to about C. andthen the sodium hydroxide-sodium propoxide mixture prepared above wasadded 0V6! a period of 1.25 hours.

The reaction mass was heated at about 97 C. for an additional period of4 hours.

The reaction mass was then cooled, washed with about 550 parts of water,the water phase was separated and the organic phase dried. While drying,a large amount of sodium chloride precipitated from the organic phase.The organic phase was filtered and dried again. About 116 parts ofproduct was recovered. The product was analyzed with the followingresult:

Phosphorus=20.1 Weight percent Nitrogen=9 weight percent Averagemolecular weight=957 Viscosity=4592 centipoises Inorganic chloride=0.09weight percent Total chloride=2.41 weight percent The analysis indicatesthe product was cross-linked with P-O'P bonds. In contrast,phosphonitrilate polymer prepared without sodium hydroxide according tothe above procedure, has a molecular weight of about 600, viscosity ofabout 80 centipoises and phosphorus content of about 19 weight percent.If the product had been pure oxygen cross-linked cyclic trimerichexapropoxyphosphazene, the molecular weight should be about 1080.

Similar results can be obtained when the propanol is replaced withmethanol, ethanol, n-butanol, hexanol, phenol, mixtures thereof, and thelike.

Similar materials are obtained when from about 0.1 to about weightpercent sodium hydroxide is used. Crosslinked phosphonitrilate polymershaving the following characteristics are within the scope of thisinvention:

Viscosity=1000-50,000 centipoises Phosphorus=20-26 Weight percentAverage molecular weight=8002000 A preferred cross-linkedphosphonitrilate composition of this invention has the followinganalysis:

Viscosity: 15,000 centipoises Phosphorus=22 weight percent Residualchloride=0.5 weight percent Residual solvent=0.5 weight percent AcidNo.=0.1

Average molecular weight=about 1200 Color Gardner==8 Phosphonitrilatepolymers prepared by the process of this invention can be used as flameretardant agents. For example, the above products can be used as a flameretardant in polyester. In addition, those compounds are very useful asfire retardants for cellulose materials, including fibers, filaments,and fabrics.

'Ihese materials may be applied to the cellulose by dipping, spraying,or other means utilized for treating the surface. Alternatively, forrayon and other regenerated cellulosics, one or more of the materialsmay be impregnated or added to the product by incorporation in theviscose prior to spinning. The amount of phosphonitrilic polymer flameretardant dispersed in the regenerated cellulose will vary from about 1to about 30 weight percent and preferably from about 2 to about 20weight percent based on the weight of the filament.

For impregnation prior to spinning and the finished materials, one mayproceed according to the teachings of Godfrey US. 3,455,713. That patentis incorporated by reference herein as if fully set forth. Accordingly,one method of preparing cellulose filaments and filamentary articlesaccording to this invention is to use the flame retardants providedherein according to the method set forth in Godfrey supra. Likewise, theinstant invention provides regenerated cellulose filaments andfilamentary articles prepared from the flame retardants, herein pro- 6vided as incorporated utilizing the techniques set forth by Godfrey.

This invention can be extended to preparation and use of materials madeby the above procedures Where the alkanols or polyols are substituted byhalogen, e.g. chlorine and bromine. Suitable monohydric alcohols forthis embodiment are made from epichloroor epibromohydrin. Likewise, 2,3dichloropropanol, and 2,3-dibromopropanol are suitable.

Likewise, this invention can be extended to preparation and use ofmaterials made by the above procedure where a monohydroxy phenol issubstituted for all or part of the monohydric alcohol. Phenol itself ispreferred as are the brominated phenols.

I claim:

1. A process for preparing a phosphonitrilate polymer having an averagemolecular Weight of from about 800 to about 2000 comprising reacting ata temperature of from about 55 to about C. for a period of from about0.5 to about 10 hours in a hot inert solvent a cyclic oligomericchlorophosphazene having the general formula 01 iii wherein a is atleast 3 with from about 5 to about 15 weight percent excess of a mixtureof an alkali metal alcoholate and from about 0.1 to about 10 percent byweight of an alkali metal hydroxide based on said alcoholate.

2. A process of claim 1 wherein said alkali metal hydroxide is presentat from about 2 to about 6 percent by weight based on said alcoholate.

3. A process of claim 1 wherein said reacting is characterized by theslow addition of said alkali metal alcoholate and said alkali metalhydroxide to said chlorophosphazene.

4. Regenerating cellulose filaments and filamentary articles, saidfilaments having dispersed therein a flame retardant amount ofphosphonitrilate polymer produced by the process of claim 1.

5. A method of preparing flame retardant regenerated cellulose filamentwhich comprises mixing viscose and a flame retardant amount of aphosphonitrilate polymer produced by the process of claim 1, shaping themixture into a filament, and coagulating and regenerating said filament.

6. A phosphonitrilate polymer produced by the process of claim 1.

7. A process of claim 1 wherein the alkali metal of said alkali metalalcoholate and said alkali metal hydroxide is sodium or potassium.

8. A process of claim 1 in which said alkali metal alcoholate has up toabout 6 carbon atoms.

References Cited UNITED STATES PATENTS 2/1968 Allcock 2602 P 4/1970Godfrey 106177 OTHER REFERENCES THEODORE MORRIS, Primary Examiner US.Cl. X.R. 260-927 N, 973

